Centrifugal sump pumps find application in a wide range of industries including mining. Mining applications for sump pumps typically include pumping a mixture of water with mineral particles of different particle sizes and densities. This mixture is commonly referred to as slurry and because it contains solids it can be very abrasive. Consequently sump pumps used in mining in most instances are constructed from wear resistant materials.
Sump pumps used in mining applications are typically mounted on beams on top of a usually wide and relative shallow sump or pit. A driving motor and pump bearings are all disposed above floor level so they are not submerged thereby ensuring longer life of these parts. The pumping elements are attached to a vertical shaft and are normally positioned at the end of a long cantilevered shaft and near to or close to the bottom of the sump. The sumps are normally located strategically within the plant and sunk below the normal floor level with shallow angled surrounding floor areas so that all leakage, spillage or slurry products will gravitate directly into the sump. Depending on the size of the sump in relation to the sump pump, the type of particles and their density and the flow rate of slurry required from the sump, some percentage of particles will naturally collect in the bottom of the sump and, once settled out of the water, they tend not be picked up again by the sump pump. Over time these particles build-up and can block the sump, particularly if the particles tend to bind together.
A conventional sump pump apparatus is illustrated in FIG. 1 which is a schematic sectional side elevation thereof. The sump pump 10 as shown includes a pump casing 12 with an impeller 14 disposed therein. The impeller 14 is operatively connected to a drive shaft 16 which in the normal pump operating position is generally vertically arranged. The drive shaft 16 is supported by a bearing assembly 18 and is operatively connected to a driving motor (not shown). A column 20 surrounds the drive shaft 16.
The pump casing 12 has two inlets to a pump chamber 21 within the casing, namely a first inlet 22 and a second inlet 24. A first strainer 26 is provided at the first inlet 22 and a second strainer 28 at the second inlet 24. A discharge pipe 25 extends from the pump casing 12. When in use the first inlet 22 and strainer 26 is positioned close to the bottom of the sump with the second inlet 24 located above it. The strainers 26, 28 function to prevent the ingress of large particulate matter into direct contact with the impeller 14 which is housed in the casing 12. Such particulates can jam the rotation of the impeller and possibly damage the impeller, leading to an early failure of the sump pump. However the impeller can still become damaged by a build-up of finer particulates within the casing.
In order to try and alleviate the problems of particle build up both in the sump pit and within the conventional sump pump housing as referred to above, it has been proposed to provide agitators which somehow extend separately into the sump pit, or another coaxial type of agitator which can be fitted to an extension shaft which projects below the second inlet 24. However the effectiveness of known agitators can vary considerably and, because agitators tend to wear rapidly, their efficiency can be rapidly diminished during use. In some circumstances, trials have been made in which the lower sump pump inlet 22 is completely closed off, with the slurry only entering via the upper pump inlet 24. While this may prevent jamming the rotation of the impeller, this may also limit the flow that can be pumped, which in turn may result in sump overflow.